Note: Descriptions are shown in the official language in which they were submitted.
CA 02836107 2013-11-14
DP 1422
A method and device for transporting a fiber contour cut out from a planar
woven fabric
in the course of producing fiber-reinforced plastic molded parts
The invention relates to a method for transporting a fiber contour cut out
from a planar
woven fabric in the course of producing fiber-reinforced plastic molded parts
according
to the preamble of claim 1 and a device according to the preamble of claim 4.
In the course of producing fiber-reinforced plastic components, which are also
known as
fiber composite components, the RTM method (resin transfer molding method), is
commonly used especially in industrial applications. The entire production
process up to
a useful plastic component consists of several individual processes occurring
successively. Preforms/prepregs are produced in a first method step. In this
preform
process, multilayer fabrics or fiber structures are usually joined in 2D (two-
dimensional),
i.e. substantially in one plane, so that the preform substantially already has
the
necessary outer contours and partly also already special and/or multiple
layers or layer
thicknesses. Preferably, a binder is introduced into the separating planes or
the
structure per se, which after its activation and/or curing leads to a fixing
of the layers
with respect to each other and therefore to the determination of a fixed 3D
form, which
is formed in the further progress of the preform process in a forming tool
(shaping die,
draping tool or the like). The preform is subsequently cut or punched out as
required at
predetermined points in order to obtain an even more precise contour. After
inserting
the preform into the press mold, the halves of the mold are closed and the
necessary
resin is injected into the cavity of the mold, wherein the resin impregnates
the fiber
structure of the preform, encloses the fibers and tightly binds them into the
matrix. The
fiber-reinforced plastic component can then be removed from the mold after
curing of
the resin.
In addition to the RTM process itself, the production of a preform already
lays the
foundation for the success of the production of a plastic component. The goal
is to
obtain a preform after the shaping of the preform from a limp material which
is
sufficiently rigid in order to be placed in a completely automatic and
operationally
reliable manner into the mold of an RTM press, or also to be transported and
stacked
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for further use. There are a large number of possibilities in the relevant
state of the art
for producing, shaping and fixing the preform.
The following method steps are known for 3D forming of multilayer two-
dimensional
cutouts from woven fabrics: woven fabrics or structures are wound off from a
roller and
placed together from several different fabrics or structures, shapes and sizes
into a
woven fabric stack, as required. It may be necessary to process or cut the
outside
contour and optionally the inside contour according to a cutting pattern of
the preform or
shaped plastic part. The cutting pattern is produced from a developed view of
the
preform or the end component. Preferably, the produced woven fabric stack
which is
substantially flat will be draped by means of a draping device, or formed into
a three-
dimensional preform. In order to obtain a substantially rigid preform from a
limp woven
fabric, it is mostly necessary that a binder is introduced between the
individual layers
and is subsequently cured.
It has been noticed that even minute faults or damage or impressions on or in
the
woven fabrics can lead to visible defects in the future plastic shaped parts.
For this
reason it is essential that during the production of a preform from several
layers,
wherein at least one layer is a fiber structure, said fiber structure is
treated with care.
The cutting or punching of a contour is usually harmless and is performed in
various
manners. For example, a contour can be cut out on a cutting table by means of
a rotary
fabric cutter from a roll of woven fabric. Subsequently, a lifting device
moves over the
cut contour and lifts the contour (the cut woven fabric or structure) and
moves the same
to a draping mold. This step can also be performed several times in order to
produce a
multilayer preform. A gluing station can be passed during or in the course of
the method
depending on the embodiment which accordingly provides contour with the
binder.
A suction gripper that has proven its worth in the meantime and is especially
based on
the Bernoulli principle is known from a large number of publications, e.g.
from DE 10
2008 023 907 Al, DE 10 2008 062 343 Al or DE 103 47 545 Al. It is a common
feature
in all these suction grippers that the operation is not performed with vacuum
but with
compressed air, and a workpiece (in the present case a limp woven fabric or
contour)
can be lifted. It is understood that these suction grippers are connected to
respective
manipulators (three-axis moving device, industrial robot or the like) with an
interface.
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It is disadvantageous in this kind of suction grippers that they still leave
impressions on
the woven fabrics to be lifted, as is shown in a slightly exaggerated manner
in Fig. 1 in
respect of the state of the art. The contour is drawn into the flow space
necessary for
the Bernoulli effect by the incoming compressed air and the resulting
Bernoulli effect.
This leads to displacements of the fiber structure or threads within the fiber
structure,
which may certainly be recognizable in the future plastic shaped part. It has
also been
noticed that especially the circular external shape of the suction gripper
also leaves a
mostly circular impression on the woven fabric.
It was noticed at the same time that most cutting devices are not always 100%
successful in severing woven fabric on the cutting table. It may also occur
that the
woven fabric is damaged not only during the fixing and lifting of the fiber
structure by the
suction gripper but also by residual connections which draw on the cut contour
during
lifting and warp the woven fabric of the contour, and that further the woven
fabric is
damaged in this way or even displaced, which again leads to problems in the
next
following cutting process for the next contour. In addition to erroneous cuts,
defective
contour shapes can also occur when folds are formed, thereby producing a
defective
preform.
It is the object of the invention to provide a method and device with which a
contour that
has been cut out can securely be lifted and displaced in a simple and secure
manner as
compared to the state of the art, wherein cutting errors on the contour of the
woven
fabric have no effects on the further production process and the woven fabric
is not
damaged during pickup and transportation. Furthermore, it shall advantageously
be
prevented that the fiber structure remaining on the cutting table is damaged
by the
removal of the contour and/or is subjected to changes in its position, thereby
preventing
errors in contours to be cut subsequently in a sufficiently secure way.
The term of fiber contour for a fiber structure to be cut out and to be
manipulated will be
used below. The term of contour relates below to the external shape of the
woven fabric
that has been cut out and accordingly also to the external shape of the
support and/or
retaining plate. The entire structure concerning fixing and lifting shall
refer to the suction
gripper, wherein the suction device could also be present in a larger number
in the
suction gripper, according to the predetermined fiber contour.
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This object is achieved by the method in such a way that a fiber contour is
cut out on a
cutting table from a flat woven fabric by means of a cutting device by forming
a
separating cut, and subsequently a suction gripper moves over the fiber
contour and
brings a surface of the transport plate in contact with the cut-out fiber
contour and a
retaining plate in contact with the flat woven fabric, and wherein the fiber
contour is
fastened to the transport plate by means of suction devices arranged on the
second
surface side of the transport plate and through-holes in the transport plate
which
correspond to the suction devices and is lifted from the cutting table, while
the retaining
plate fixes the woven fabric to the cutting table, and wherein the suction
gripper and/or
the retaining plate is/are lifted from the cutting table after the lifting of
the transport plate
and the fiber contour is transported by the suction gripper.
The object is achieved by a device in such a way that at least one suction
device is
arranged on a suction gripper on a first surface side of a transport plate,
wherein the
second surface side is suitable for the suction of a fiber contour through the
through-
holes in the transport plate which correspond to the suction device, and the
transport
plate is substantially arranged in its external contour like the cut-out fiber
contour,
wherein the retaining plate, when arranged in one plane with the transport
plate,
encloses said transport plate substantially by forming a gap, and wherein the
retaining
plate and/or the transport plate is displaceable by means of at least one
suitable
actuating device in at least two planes which differ from one another.
Furthermore, this leads to advantages in that the fiber contour can be
transported in a
careful manner and any potential residual connections in the separating cut
can be
severed by means of retaining without significantly distorting the woven
fabric or the
fiber contour.
It is further advantageous if the suction devices operate according to the
Bernoulli
principle and the air flows of the suction devices produced by the supply of
compressed
air are substantially guided away from the separating cut of the fiber contour
or the
woven fabric through the transport plate and the retaining plate without
causing any
swirling on the separating cuts. It is further advantageous that the fiber
contour is
spread out in a flat manner in the course of making contact with the transport
plate and
may thus be placed in a better way on a scrim for a preform or is better
suitable for
gluing. It can further be provided to have the fiber contour resting in a flat
manner on the
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transport plate monitored with automatic imaging or other suitable monitoring
devices
during transport in order to determine whether the quality is sufficient
further processing.
It is obvious that the suction device can also be operated with negative
pressure, but
preferably with compressed air.
The device is especially suitable for performing the method, but can also be
operated
independently.
It is now advantageously prevented that damage on the fiber structure
remaining on the
cutting table and on the fiber contour to be lifted will occur, because during
the lifting a
retaining plate close to the contour or corresponding to the contour will
press the
remaining woven fabric onto the base or the cutting table. As a result, damage
on the
fiber contour to be lifted is also prevented and the fiber contour is
substantially held in
one plane on the transport plate and in the suction gripper by the suction
devices. It is
further advantageous that the retainer prevents that the remaining woven
fabric on the
cutting table is lifted or swirled by the suction apparatuses or their air
flows beyond the
transport plate. It is further prevented in a similarly advantageous manner as
a result of
the configuration of the transport plate which is close to the contour
according to the
cut-out fiber contour that the air flows of the suction apparatuses will fray
the lifted fiber
contour at its edges on the separating cut. The same also applies to the
remaining
woven fabric on the cutting table, which is especially advantageous in an
optimized
cutting arrangement of the contours when a separating cut forms the edge of
two
different fiber contours for example, wherein they are to be lifted
successively.
By using a suction apparatus operated by compressed air, air is drawn to the
surface
side of the suction devices through the through-holes in the transport plate,
which
substantially occurs according to the Bernoulli-Venturi principle. The through-
holes can
be suitable holes or oblong holes, whose arrangement or size can be determined
by
tests and may depend among other things on the type of the woven fabric, the
strength
of the air flows and other factors.
Further advantageous measures and embodiments of the subject matter of the
invention are provided in the dependent claims and are described in the
description with
the drawings below, wherein:
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Fig. 1 shows a sectional view of a conventional suction device according to
the state of
the art when receiving a limp fabric;
Fig. 2 shows a further sectional view of a suction device in accordance with
the
invention with a transport plate during the accommodation of a limp fabric;
Fig. 3 shows a sectional top view of a contour of a transport plate with
suction devices
arranged thereon;
Fig. 4 shows a further sectional top view of a contour of a transport plate
with suction
devices according to Fig. 3 which are arranged thereon, with additional
illustration of a
corresponding retaining plate and a gap arranged in between;
Fig. 5 shows an enlarged view of a lifting apparatus according to Fig. 3 in a
lateral
sectional view with additional illustration of the actuating devices for the
retaining plate.
Fig. 1 shows a sectional view of a conventional suction device according to
the state of
the art when receiving a limp fabric, which deforms under the Bernoulli effect
and is
drawn into the necessary cavities for the suction device 1. The illustration
also clearly
shows that the support bodies 11 are arranged on the outer circumference of
the
suction device 1 and are capable of leaving impressions on the fiber contour
3. The air
flows of the compressed air supply 2 symbolized by the arrows.
Fig. 2 shows how the flat transport plate 4, which clearly protrudes beyond
the outer
contour of the suction device 1, prevents that the sensitive fiber contour 3
will deform. In
order to still allow the effect of the suction device 1 to act on the fiber
contour 3,
boreholes, oblong holes or other suitable through-holes 14 are provided in the
transport
plate 4, which are arranged in a corresponding manner to the suction device 1
so that
the passing air flow produces a kind of Venturi effect in the through holes
14, thereby
producing the adherence of the fiber contour to the transport plate 4.
Fig. 3 shows a sectional top view of a contour of a transport plate 4 with
suction devices
1 arranged thereon. As a result of the transport plate 4, the fiber contour 3
which is
situated beneath is substantially covered, wherein no through-holes 14 can be
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recognized, but which shall not exclude the potential arrangement thereof
outside of the
contact points of the suction devices 1 with the transport plate 4.
Fig. 4 shows a further sectional top view of a contour of a transport plate 4
with suction
devices 1 according to Fig. 3 which are arranged thereon, including an
additional
illustration of a corresponding retaining plate 5 and a gap 9 which is formed
in between.
Preferably, the gap 9 substantially emulates the contour of the fiber contour
3, so that
when compressed air exits from the suction devices the separating cuts 12
between the
fiber contour 3 and the woven fabric 6 cannot be attacked by the air flows.
Fig. 5 shows an enlarged view of a lifting device or a suction gripper
according to Fig. 3
in a lateral sectional view with additional illustration of the exemplary
actuating
apparatuses 8 for the retaining plate 5. In the present view, the fiber
contour 3 is fixed
by the transport plate 4 and the region of the woven fabric 6 adjacent to the
separating
cuts 12 is fixed with the retaining plate 5 to the cutting table 7.
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List of reference numerals: DP 1422
1 Suction device
2 Compressed air supply
3 Fiber contour
4 Transport plate
Retaining plate
6 Woven fabric
7 Cutting table
8 Actuating apparatus
9 Gap
Interface
11 Support body
12 Separating cut
13
14 Through-holes
8
